Current dental practices make use of intraoral dental retraction cords during both restorative and impression taking operations (i.e. prosthetic dentistry). Such cords are often referred to as gingival tissue retraction cords.
When restoration of dental caries (cavities) at, near, or below the marginal attached gingiva (gumline) is required, dentists typically distend and retract the gingival or periodontal sulcus (eyelid-like space below the top of the gumline) in order to achieve sufficient access to the carious lesion. Thereafter, the practitioner generally removes the dental caries by drilling and fills the cleaned out hole in the tooth by way of a VLC composite resin or amalgam.
The distention of the periodontal sulcus is typically achieved by way of a rubber dam and corresponding clamp. Alternatively a conventional woven or braided gingival retraction cord is used. A significant drawback associated with the use of a rubber dam and corresponding clamp(s) is that they often produce periodontal tissue trauma and bleeding which compromise the restorative result. The problems which arise within respect to the use of conventional woven or braided cords is discussed below.
Prosthetic dentistry is known in the art to involve the construction of crowns, caps, partial dentures, full dentures, implants, and fixed bridgework. The practice of prosthetic dentistry often requires the taking of accurate impressions (or molds) of a particular tooth, teeth, or implant for which prosthetics will be fabricated at a dental laboratory. At the interface (or limit line) of the tooth (or root, or implant) surface to be worked on and the gingival margin (gumline), it is important that prior to impression taking, the gingival sulcus be reflected or retracted in order to register an accurate impression of the prepared tooth (or root, or implant) structure.
This type of refraction is typically accomplished by way of conventional dental periodontal sulcular retraction cord (or gingival retraction cord). In short, a small diameter (e.g. 1-2 mm dia.) braided or woven cotton cord is pressed into the periodontal sulcus prior to flowing the impression material onto the tooth, teeth, or implant. Conventional retraction cord is often impregnated with certain chemicals (e.g. racemic epinephrine, aluminum choride, or adrenalin).
In use, this conventional retraction cord is typically unwound from a spool or withdrawn from a container. The dental practitioner estimates the length of cord required for the particular application and snips the desired length of cord from the spool. The practitioner then wraps the cord around the tooth and either ties a knot to hold the cord in position on the cervical portion of the tooth, or overlays several turns of the cord on the tooth to hold the cord in place. The practitioner then packs the cord into the gingival sulcus so as to reflect or retract the gum tissue away from the tooth structure thereby enabling the accurate taking of an impression of the tooth inclusive of its cervical portion in prosthetic dentistry for example.
Practitioners often use small conventional dental instruments to position the cord in the periodontal space. Once the impression material hardens and is removed from the tooth and mouth or the filling is in place, the retraction cord is removed from the periodontal space and discarded. It is noted that the "periodontal space," "periodontal sulcus," "marginal periodontal tissue," and "gingival sulcus" are synonymous terms well-known in the art, and their well-known meaning is adopted here.
Problems arise in the use of these woven or braided cords whether used in the process of drilling and filling dental caries or in the other processes discussed above. For example, it is often the case that the insertion and removal of conventional woven or braided string-like gingival retraction cord produces gingival tissue trauma and periodontal sulcular bleeding thereby compromising the accuracy of the impression or filling and causing post operative discomfort to the patient. Furthermore, some patients are chemically sensitive to conventional chemically impregnated retraction cords and experience discomforting side effects as a result thereof.
Another problem associated with conventional woven or braided string-like dental retraction cords is their tendency to physically attach or stick to dental restorative and impression taking materials. When such sticking occurs, it becomes extremely difficult for the practitioner to remove the cord from both the periodontal sulcus and the finished restoration and/or impression taking material.
Yet another problem with conventional string-like woven or braided retraction cords is their tendency to shred or tear during both insertion and removal from the periodontal sulcus. Such shredding and tearing often produces undesirable gingival sulcular tissue trauma, bleeding, and post operative patient discomfort. Additionally, torn or shredded pieces of the cord may be left behind inside the patient's mouth or gumline leading to the possibility of infection.
U.S. Pat. No. 4,892,482 discloses a gingival tissue dental retraction cord made of a plurality of strands including a central stiffener strand of, for example, copper wire or other material which provides the cord with deformability. Unfortunately, the construction of the dental retraction cord of this patent renders it subject to the above-mentioned disadvantages associated with other conventional retraction cords.
U.S. Pat. No. 4,871,311 discloses a dental retraction cord for uncovering and draining the preparation limit line of a tooth where the tooth emerges from the gum tissue during dental procedures such as the taking of dental impressions, the cementing of crowns, and the performance of conservative caries therapy (i.e. the type uses contemplated herein by the subject invention). The retraction cord of this patent, after being inserted into the periodonal sulcus, swells and thereby mechanically uncovers the preparation limit line and tends to stop bleeding of the gum tissue. The preferred material for making the swelling cord of this patent is a super absorbent swelling material made of an acrylic fiber having a skin constituted by a co-polymer of polyacrylic acid and polyammonium acrylate and a core of polyacrylonitrile, in which the skin provides about thirty percent of the weight of the fiber. Unfortunately, the cord of this patent, both before and after swelling, is susceptible to the disadvantages and problems set forth above.
U.S. Pat. No. 4,321,038 discloses a braided gingival retraction cord which is subject to the above-described disadvantages. The cord of this patent includes strands of fluid absorbent yarns or thread, such as cotton. Following fabrication, the braided cord of U.S. Pat. No. 4,321,038 is passed through a chemically impregnating solution containing a concentration of such chemicals as epinephrine, alum, aluminum chloride, or mixtures thereof, to saturate the cord.
U.S. Pat. No. 5,033,488 discloses a porous, high strength dental floss made of expanded polytetrafluoroethylene (i.e. PTFE or "Teflon.TM."). The dental floss of this patent, coated with microcrystalline wax, is made using expanded PTFE (Teflon) so as to allow the dental floss to pass smoothly through the narrow spaces defined between adjacent teeth.
It is also known to use PTFE in clinical dentistry for periodontal regeneration surgical procedures. For example, GORE-TEX.TM. e-PTFE is often applied to periodontal osseous defects such as those which can occur around molar teeth or endosseous implants. Such material is used to guide regeneration of new bone around teeth or dental implants.
This GORE-TEX.TM. material is also used for guided tissue regeneration by draping the material over a surgically exposed tooth and cleansed peridontal site (e.g. a Class I furcation defect) so as to allow for regrowth of healthy periodontal tissue. Periodontal regeneration often occurs in this space. After removal of the PTFE material, newly regenerated periodontal fibers provide additional tooth support. These uses of e-PTFE, however, are not related to gingival retraction cord.
It is apparent from the above that there exists a need in the art for a dental retraction cord or tape which (1) is resistant to shredding and tearing; (2) is resistant to sticking to dental restorative and impression taking materials; and (3) reduces tissue trauma, bleeding, and post operative patient discomfort. Furthermore, a need arises in the art for a dental retraction cord free of chemical impregnation so as to permit the cord to be used during dental procedures carried out upon chemically sensitive patients.
It is the purpose of this invention to fulfill the above-described needs in the art, as well as other needs which will become apparent to the skilled artisan from the following detailed description of this invention.